Re: Special Memory Constraint [was Re: Indirect memory addresses vs. lra]

[Vladimir Makarov <vmakarov@redhat.com>]

On 2019-08-19 3:35 a.m., John Darrington wrote:
> On Fri, Aug 16, 2019 at 10:50:13AM -0400, Vladimir Makarov wrote:
>       
>       
>       No I meant something like that
>       
>       (define_special_memory_constraint "a" ...)
>       (define_predicate "my_special_predicate" ...
>       		
>        {
>          if (lra_in_progress_p)
>            return REG_P (op) && REGNO (op) >= FIRST_PSEUDO_REGISTER && reg_renumber[REGNO(op)] < 0;
>          return true if memory with sp addressing;
>       })
>       
>       I think LRA spills pseudo-register and it will be memory addressed by sp
>       at the end of LRA.
>
> What I've done is this:
>
> (define_predicate "my_special_predicate"
> 		    (match_operand 0 "memory_operand")
>   {
>     debug_rtx (op);
>     gcc_assert (MEM_P (op));
>     op = XEXP (op, 0);
>     if (GET_CODE (op) == PLUS)
>       op = XEXP (op, 0);
>
>     if (lra_in_progress)
>       {
>         fprintf (stderr, "%s:%d\n", __FILE__, __LINE__);
>         return REG_P (op) && REGNO (op) >= FIRST_PSEUDO_REGISTER && reg_renumber[REGNO(op)] < 0;
>       }
>
>
>     if (REG_P (op))
>       {
>         int regno = REGNO (op);
>         return (regno == 10); // register is the stack pointer
>       }
>
>     return true;
>   })
>
>   (and many variations)  Unfortunately, any moderately complicated input
>   still results in a (mem (reg) ) insn repeatedly entering the
>   lra_in_progress case and returning false, and eventually terminating with
>       
>   "internal compiler error: maximum number of generated reload insns per insn achieved (90)"
>
>
> Any other ideas?
   As I remember there were a few other ideas from Richard Biener and 
Segher Boessenkool.  I also proposed to add a new address register which 
will be always a fixed stack memory slot at the end. Unfortunately I am 
not familiar with the target and the port to say in details how to do 
it.  But I think it is worth to try.